If the point of requiring background checks before selling guns is to keep firearms out of the hands of people who aren’t supposed to have them, Maine, along with most other states, is failing. That’s because an estimated 40 percent of gun sales take place online or through other venues that do not require background checks.

Federal and Maine law prohibits the sale of firearms to felons, domestic abusers and others deemed too dangerous to own them. But without background checks on thousands of gun sales each year, it is impossible to keep these prohibited buyers from obtaining guns.

A new analysis by Everytown for Gun Safety, the group seeking to expand background checks in Maine, found that more than 3,000 guns are advertised for sale in Maine each year through entities that would not trigger federal background checks.

This huge hole in federal law should concern everyone but especially gun owners who follow the law. In fact, it does. Polls consistently have found that about 90 percent of Americans and nearly as many gun owners support universal background checks for gun purchases.

Federal law requires all purchasers of firearms through licensed dealers pass a background check. That check certifies that the purchaser is not a felon or domestic violence offender prohibited from purchasing a firearm.

But as many as 40 percent of gun sales are so-called private sales that do not require background checks. Guns sold over the internet or through ads in publications like Uncle Henry’s fall into this category. According a 2010 article in the New England Journal of Medicine, “some 85 percent of all guns used in crimes and then recovered by law-enforcement agencies have been sold at least once by private parties.”

According to data from the Bureau of Alcohol, Tobacco, Firearms and Explosives, Maine was the second largest out-of-state source of guns seized in Massachusetts last year, behind New Hampshire. In Massachusetts, every gun buyer must have a license to carry from local police, which requires a background check. In addition, private gun sales must be recorded and reported to the state within seven days. To avoid these requirements, criminals head north, where “it’s an open-air bazaar, in some sense, for firearms,” Capt. Mark O’Toole, who leads the Lynn Police Department’s Criminal Investigations Unit, told Boston radio station WBUR.

In Maine, background checks blocked 5,501 gun sales between 1998 and 2014, data from the FBI show. Half of the denials happened because the potential buyers had criminal convictions. Domestic violence convictions were the second most common reason for denial.

These data show that background checks work. But they’re required for too few gun sales in Maine, allowing prohibited buyers to turn easily to other venues to purchase firearms.

More than 2,300 gun ads for sales that would require no background checks appear in the Uncle Henry’s print catalog every year. Another 500 Maine gun ads appear on Armslist, a firearms sales website, according to Everytown’s research. These are just two of the places where sellers in Maine advertise private gun sales.

Subjecting these sales to background check requirements is a needed safeguard that simply makes sense.

The Bangor Daily News editorial board members are Publisher Richard J. Warren, Opinion Editor Susan Young, Deputy Opinion Editor Matt Junker and BDN President Todd Benoit. Young has worked for the BDN...